Long-lived protective immunity to Listeria is conferred by immunization with particulate or soluble listerial antigen preparations coadministered with IL-12.

The ability of IL-12 to promote the development of Th1-type immune responses, and thus promote cellular immunity, has been well documented. In a previous report, we showed that coadministration of IL-12 with heat-killed Listeria monocytogenes elicited intense antigen-specific T cell responses that conferred protective listerial immunity. Herein, we have extended those studies by demonstrating that multiple injections of heat-killed L. monocytogenes and IL-12 elicit memory responses that confer long-lived (> or = 3 months) protective immunity and that immunity can be transferred adoptively with cells from immunized mice injected into naive mice. These studies have also demonstrated that the powerful adjuvanticity of IL-12 is observed with soluble as well as particulate immunogens and is operative in mouse strains that have different MHC haplotypes. These findings suggest that IL-12 may be a useful adjuvant component of vaccines for a wide variety of pathogens in animal and human systems.